(a) Field of the Invention
The present invention relates to a magnetic disk and method of manufacturing the magnetic disk, and more particularly to a magnetic disk suitable for optimization of the floating posture of the magnetic head and in which the electromagnetic conversion characteristic and the signal-to-noise ratio of reproduced signal are improved through the improvement in strength of the magnetic film on the magnetic disk.
(b) Related Art Statement
As shown in FIG. 1, a conventional magnetic disk is known which has a substrate 1 on which there is formed a resin layer 2 on which there is formed a magnetic film 3 on which a lubricant layer 7 is applied. The magnetic film 3 is composed of a magnetic powder 4, fillers 5 and binder 6 as shown. Normally, a magnetic iron oxide is used to produce the magnetic powder and a single-crystal alumina is used to produce the fillers 5. Also the binder 6 is usually made of a thermosetting resin.
The mixing of the fillers 5 in the magnetic film 3 in the above-mentioned conventional magnetic disk is intended to increase the strength of the magnetic film 3 and improve the durability of the magnetic film 3. From another point of view, however, the mixing of the fillers 5 in the magnetic film 3 will possibly cause a defect in the magnetic film 3. Thus the fillers 5 will possibly introduce noise to the reproduced signal, degrade the signal-to-noise ratio of the reproduced signal and degrade the electromagnetic conversion characteristic of the magnetic disk. Especially in case a filler 5 protrudes from the surface of the magnetic film 3 as shown in FIG. 1, the problem due to the above-mentioned fillers 5 will be remarkably difficult.
Also in case a magnetic disk is produced of which the thickness of the magnetic film 3 is reduced to increase the recording density, a filler 5 will protrude high from the surface of the magnetic film 3 as shown in FIG. 2. This is because the uniform reduction in particle size of many fillers 5 is technically limited and the particle size of the fillers 5 is large as compared with the thickness of the magnetic film 3. Therefore, with the conventional technique, it is difficult to produce a magnetic disk of which the magnetic film 3 is reduced in thickness. Also if the filler 5 protrudes high from the magnetic film 3, the filler 5 will introduce noise to the reproduced signal, lower the signal-to-noise ratio of the reproduced signal and degrade the electromagnetic conversion characteristic of the magnetic disk. In addition, if the filler 5 is protruded high from the magnetic film 3, the magnetic head will collide with the filler 5 when recording and/or reproduction is made to and from the magnetic disk and adversely affect the floating posture of the magnetic head. As a result, the electromagnetic conversion characteristic of the magnetic disk is further degraded.
To solve the above-mentioned problems, it is necessary to limit the height of the filler 5 to a predetermined value with reference to the surface of the resin layer 2 and, for example, to manufacture a magnetic disk for the filler 5 not to protrude too much from the surface of the magnetic film 3. With the conventional method of producing a magnetic disk, however, it is very difficult to control the protruded height of the filler from the surface of the magnetic film 3 and the height of the filler from the resin layer 2 in the magnetic film 3. The above-mentioned problem has become remarkably difficult as an increasingly reduced thickness of the magnetic film 3 is required for the magnetic disks.
As a conventional technique related with the present invention, an invention is known from the Japanese Unexamined Patent Publication (Kokai) No. 61-29414 in which a magnetic disk is disclosed in which fine particles are diffused in a plated layer formed on a substrate and a magnetic film is formed on the plated layer. However, the formation of the plated layer in which fine particles are contained is intended for reducing the manufacturing costs by thinning the plated layer through reinforcement of the plated layer itself, and for protecting the magnetic film by laying some of the fine particles as exposed on the surface of the magnetic film.
On the contrary, the present invention proposes a magnetic disk in which the resin layer 2 is formed, not the plated layer, on the substrate, and a method of manufacturing such magnetic disks, in which the protruded height of the filler can be easily controlled. Therefore, the present invention is basically different from the invention disclosed in the above-mentioned Japanese Unexamined Patent Publication.